It is the purpose of this project to study the pathogenesis of intestinal amebiasis, sequentially, at the ultrastructural level, to ascertain the mechanism of epithelial penetration by Entamoeba histolytica and to visualize and describe the cellular interactions and effects of ameba on organelles of all intestinal tissue cells and wandering inflammatory cellular elements, from the time ameba become established in the gut lumen through the process of ulcer formation. It is the purpose of the sub-project to compare the virulence of various strains of Entamoeba histolytica by intrahepatic inoculation of golden hamsters, to make histopathological evaluations and comparisons on the effects of such inoculations and to determine the relevance of certain endogenous viruses to the pathologic processes and virulence of particular strains of ameba.